1. Field of the Invention
The present invention relates to an input-output circuit that is disposed between a connector and an internal circuit.
2. Description of the Related Art
Recently, smartphones have been rapidly come into wide use. In many smartphones, in order to improve the designability or decrease the circuit scale, a connector is attempted to be used in common. For example, models only having a micro-USB connector are also available in the market. In such models, in addition to power feeding and data communication, audio signals are transmitted or received through one micro-USB connector. Such connector sharing has been attempted also in other mobile devices such as a cellular phone, a small-sized PC, a digital camera, a portable music player, an IC recorder, and a game machine.
While there is such a trend of the connector sharing, the number of kinds of accessory devices connected to each mobile device has been increased every year. In order to accurately recognize a variety of accessory devices, it is necessary to precisely measure the resistance value of each accessory device, and thus a circuit for that purpose is required.